1. Technical Field
The present invention relates to a projector-type vehicle headlamp, and particularly to a vehicle headlamp configured to illuminate light for forming a low-beam light distribution pattern.
2. Background
A vehicle headlamp is generally configured such that a projection lens is disposed on an optical axis extending in a longitudinal direction of a vehicle, a light source is disposed to the rear of a rear focal point of the projection lens, and light from the light source is reflected close to the optical axis by a reflector.
Japanese Patent Publication JP-A-2001-76510 discloses a lamp configuration wherein a shade for shielding a portion of light reflected by the reflector is disposed in the vicinity of a rear focal point of the projection lens.
In addition, Japanese Patent Publication JP-A-4-39137 discloses a lamp configuration with an annular prismatic lens for refracting direct light that has traveled from the light source toward the outside in the widthwise direction of the vehicle, to approach an optical axis. The lens is disposed between the projection lens and the reflector.
When the lamp configuration disclosed in Japanese Patent Publication JP-A-2001-76510 is employed, light for forming a low-beam light distribution pattern can be illuminated. However, the luminous energy of light illuminated forward of the vehicle is reduced by the quantity of light shielded by the shade.
When this lamp includes the annular translucent member as disclosed in Japanese Patent Publication JP-A-4-39137, the direct light from the light source toward the space beyond the outer periphery of the projection lens illuminates forward of the lamp, thereby enabling effective utilization of light source luminous flux. Accordingly, the luminous energy of light illuminated forward of the vehicle can be increased.
However, the prismatic lens disclosed in Japanese Patent Publication JP-A-4-39137 has an annular shape. Accordingly, light that has exited from the prismatic lens cannot be controlled with high accuracy. Furthermore, a portion of the exited light becomes upward-illuminating light, thereby hindering formation of the low-beam light distribution pattern, which is problematic.